Delta-9-Tetrahydrocannabinol (THC) is the principal behaviorally active compound in marijuana, a substance that is used by millions of young Americans. It and other cannabinoids are highly lipophilic compounds that can affect the fluidity or lipid ordering of biological membranes. This has led us to the hypothesis that membranes are recognition sites for the cannabinoids and that tolerance to THC results in changes in the physical properties or lipid composition of these membranes. In addition, we have proposed that THC alters the functioning of neuronal membranes including their ability to act as a semi-permeable barrier to ions and maintain a transmembrane potential difference. The following experiments will be carried out to test these hypotheses. Studies of membrane fluidity using fluorescence polarization techniques will be continued. Cannabinoid effects on synapitc plasma membranes (SPM) from six brain areas will be compared using two probes; DPH which primarily monitors the interior acyl chain tail region and TMA-DPH which monitors movement near the surface of the membrane. The effects of chronic treatment with THC on the fluidity of SPM from the six brain areas will also be examined as will the composition of the SPM lipids in order to determine if tolerance occurs at the membrane level. The effects of cannabinoids on lateral motion within membranes will also be determined by measuring pyrene excimer formation. Changes in lateral motion within the membrane may be involved in the effects of the cannabinoids on enzyme systems such as receptor-stimulated adenylate cyclase. THC decreases the synaptosomal accumulation of tetraphenylphosphonium (TPP) indicating that synaptosomes are depolarized by THC. Our studies of this phenomenon will be expanded to include examining the effects of other cannabinoids and whether or not tolerance occurs. Mechanisms underlying the THC induced change in membrane potential as measured using TPP accumulation will be studied using drugs to modify the transport of ions across membranes. In addition, the effects of the cannabinoids on synaptosomal ion flux will be measured directly. The completion of the proposed studies should enable us to more fully understand the role of membrane perturbation in the neurochemical effects of the cannabinoids and in the development of tolerance.